We analyzed the structure of the MOOC ecosystem from the perspective of two aggregators, "Class Central" and "MOOC List," which gather information on thousands of courses. Their datasets, which range from 2012 to 2015, enabled us to underline the contrast between most important platforms such as Coursera or edX, and smaller scale platforms, notably their European counterparts. Both the number of courses produced by institution and the estimated workload for each course are higher in North America, suggesting that the strategies of institutions of higher education differed between both continents. Finally, we show that course duration decreased over the years, and suggest that it represented a strategy to tackle low completion rates.